Macrocyclic vinyl polymers have long elicited intense interest due to their unique properties when compared to linear polymer analogs. For example, beyond differences such as increased glass transition temperature and reduced viscosity, cyclic vinyl polymers show improved energy transfer between pendant groups compared to linear analogs, owing to their spatial orientation around the ring (especially pronounced at lower degrees of polymerization), making them potentially valuable in light harvesting systems.
Although macrocyclic vinyl polymers are desirable, a straightforward and efficient route to their synthesis has remained elusive. Specifically, while the direct synthesis of macrocyclic polymers has been accomplished by polyhomologation and ring opening metathesis polymerization (ROMP) using a cyclic derivative of Grubbs' catalyst, traditional methods for the synthesis of macrocyclic vinyl polymers tend to rely on the production of a linear precursor and subsequent end-to-end coupling. For example, α,ω-dilithiopolystyrene (LiPSLi) or α,ω-dipotassiopolystyrene (KPSK) are first produced and subsequently employed in two consecutive SN2 reactions with a bifunctional electrophile, the second being intramolecular when performed under high dilution (˜10−4 M). Such reactions are exceedingly difficult to perform due to the high reactivity of polymer anions. This difficulty is compounded by a cyclization reaction that requires simultaneous dilute addition of both the polymer dianion and bifunctional electrophile into a reaction mixture.
The development of controlled radical polymerization methods, especially atom transfer radical polymerization (ATRP) and nitroxide mediated polymerization (NMP), has opened the door to experimentally more lenient syntheses of well-defined telechelic linear precursors. Nevertheless, a major drawback of linear precursors is the requirement of compatibly reactive α,ω end groups, which must be installed post-polymerization. For example, intramolecular click chemistry and intramolecular ring closing metathesis has proven highly efficient in producing macrocycles, but relies on synthetic modification of polymer chains prior to employing them in cyclization reactions. This approach may create multiple problems, including, for example, the need to quantitatively modify the polymer to produce high yields of cyclic products, additional functionalization of the cyclic products as a consequence of these modifications, which may or may not be desirable. Additionally, modification of the polymer chain ends prior to coupling adds step(s) to the overall synthetic route to produce macrocycles.
Therefore, there is a need for a method of producing macrocyclic polymers that avoids the need for post-polymerization fuctionalization of the precursor to form reactive α,ω end groups to facilitate cyclization of the molecule. The present invention fulfills this need among others.